Nitric acid concentration



Jan. 24,1933. 5 F, NGLER 1,895,012

. NITRIC ACID CONCENTRATION Filed May 16, 1930 2 Sheets-Sheet l INVENTORSGML-48 Spanger TTORNE 5 1933. s. F. SPANGLER NITRIC ACID CONCENTRATIONFiled May 16, 1955'; Sheets-Sheet.

INVENTOR 5omue] F5 anger ATTOR YS Patented Jan. 24, 1933 UNITED STATESSAMUEL F. SPANGLER, OF PHILADELPHIA,

PENNSYLVANIA, ASSIGNOB TO CONSTRUCTION CORPORATION, 01! CHARLOTTE, NORTHCAROLINA, A CORPORATION OF DELAWARE NITBIC!" 1cm coxcmaanon Applicationfled Kay 16, 1930. Serial No. 452,903.

This invention relates to nitric acid conoentration, and moreparticularly to a method and means for the concentration of nitric acidby the use of a dehydrating agent such as sulphuric acid.

In a copending application of Ingenum Hechenbleikner and the presentapplicant, Serial No. 450,912 filed May 9, 1930, a nitric acidconcentration system is disclosed in which the dilute nitric acid to beconcentrated is mixed with sulphuric acid in an unheated mixer tube,after which the mixture of nitric and sulphuric acids is passe-d througha plurality of heated retort tubes or pipes. The water content of thenitric acid is 1n the main removed by the sulphuric acid, and such watervapor as may incidentally be distilled off with the nitric acid vapor isremoved from the nitric acid vapor in a dehydrating tower.

I have found that to insure uniform operation of such a concentrationsystem it is ecessary that the nitric and sulp uric acids be thoroughlymixed and not permitted to stratify in layers. Accordingly, toaccomplish thorough mixing of the acids is a primary object of myinvention, and this I have found may be one b mixing the dilute nitricacid with the su phuric acid in large volumes. In accordance with myinvention, a mixing chamber is provided which, different from thepractice set forth in the aforesaid copending application, issubstantially greater in volume than one of the retort tubes.

The mixer tube or chamber employed in the apparatus of said copending aplication is unheated. A further object of t e present invention is tomake it feasible not only to thoroughly mix the acids ina mixer chamber,but also to heat at least a portion of the mixer chamber in order toincrease the operating capacity of the plant. To fulfill this object ofmy invention the flow of nitric acid vapor from the retort tubes to thedehydrating tower is facilitated, as by increasing the cross sectionalarea of the flow space provided for the passage of such vapor, or byproviding independent flow connections, first, between the retort tubesand the dehydrating tower, and, second, between the heated mixer tubesand the dehydrating tower.

To the accomplishment of the foregoing and such other objects as willhereinafter appear, my invention consists in the nitric acidconcentration method and apparatus elements and their relation one tothe other, as hereinafter are more particularly described and sought tobe defined in the claims. The specification is accompanied by drawingswhich show the preferred embodiments of my invention, and in which:

Fig. 1 is a schematic flow diagram of a nitric acid concentration systemembodying my invention;

Fig. 2 is a portion of Fig. 1 showing a modified form of my invention;and

Fig. 3 is a ortion of Fig. 1 showing still another modi cation of theinvention.

Referring to the drawings, and more particularly to the complete fiowdiagram shown in Fig. 1, a dehydrating agent, preferably. sulphuricacid, flows from a tank S dowfnwardly through a dehydrating tower D andthence into a mixer chamber M. The dilute nitric acid to beconcentratedflows from a tank N into the heated mixer chamber M at apoint below the packing of the dehydrating tower D, and in themixerchamber M the dilute nitric acidf'is mixed with the sulphuric acid. fTheacid mixture flows downwardly through a vertically superposed bank ofretort tubes R heated by individual steam jackets. Separate bodies ofacid mixture of different strengths are retained in the retort tubes bydams located at the discharge ends thereof, as is schematically shown inthe drawings.

Nitric acid vapor is evolved from the acid mixture in the retort andmixer tubes and the water content of the dilute nitric acid is, for themost part, retained by the sulphuric acid. The nitric acid Vapor alongwith some water vapor incidentally evolved therewith flows upwardthrough the'retort tubes and upward through the mixer tubes and thenceto the dehydrating tower D. During its passage upward through the towerthe water vapor is removed by the descending sulphuric acid. Thedehydrated nitric acid vapor flows from the top of the tower downwardlythrough pipe P and then upwardly pally by the abstraction .of oxides ofnitrogen therefrom by the rising nitric acid vapor. From the bleacherpipe the concentrated nitric acid flows into a water-jacketed collectingtube T from which the acid is led through a pipe 10 to any suitablestorage tank.

The sulphuric acid leaving the retort tubes R, diluted by theacquisition of water, flows into a cooler 12 from which it is ledthrough1 a pipe 14 to any conventional concentractor after which it is returnedto the sulphuric acid supply tank S. A suction fan 16 is pre.

ferably provided at the outlet of the condenser C in order to drawundissolved oxides of nitrogen together with air which may have leakedinto the system out of the retort tubes, mixer chamber, dehydrator andcondenser. The fan exhaust may, if desired, be led to one of theabsorption towers in which artificially-manufactured oxides of nitrogenare initially absorbed to manufacture the dilutenitric acid whicheventually is concentrated by the apparatus of the present invention.The fan 16 maintains a slight vacuum throughout the concentrator systemwhich aids in the desired distillation of nitric acid vapor in theretort and mixer tubes, and, consequently, the pressure in the system,as indicated by the monometers 18, should preferably be at leastslightlynegative.

The arrangement so far described corresponds generallyiwith thatdisclosed in the copending application before mentioned, and in thepresent arrangement, as in that arrangement, it is preferable that eachof the retort tubes 21, 22, 23, 24, 25 and 26 be .provided withindependent heating means, here exemplified by the steam jackets 31, 32,33, 34 35 and 36, which should preferably be fed with steam throughindependent pipes so as to make possible temperature control in each ofthe tubes so as to obtain the proper temperature for optimum yield. Itwill be understood that electrical heating, either by resistance orinduction, may \equally well be employed.

' Each of the tubes is provided at its discharge end with a dam 41, 42,43, 44, 45 and 46 for establishing the liquid level in the tubes, andthese should preferably be readily interchangeable or adjustable so thatthe liquid level in each ofthe tubes may be determined independently ofthat in the other tubes. In general, it is found that the level in theupper tubes should be lower than that in the lower tubes in order toincrease the andregardless of whether one. or two tubes are used, theincreased volume is obtained by establishing a relatively high liquidlevel in the mixer tubes. The present arrangement improves upon theprior system, secondly, in the provision of steam ackets or similarheating means for heating the mixer chamber so that the mixer chamberitself may be used to romote the evolution of nitric acid vapor.

Jither or both of these features would, in the prior system, too greatlydiminish the vapor space above the liquid.

In accordance with the present invention these difiiculties are overcomeby the provision of'a bypass connection 50 which facilitates the passageof nitric acid vapor from the retort tubes R directly to the dehydratingtower D. The nitric acid vapor evolved in the heated mixer chamber isconducted to the dehydrating tower D by an independent connection 52which also serves to guide the sulphuric acid descending from the tank Sinto the mixer chamber M where it is mixed with the dilute nitric acidentering the mixer chamber M from the tank N. The provision of thebypass connection ,50 and its relation to the connection 52 constitutesa third important distinction between the present arrangement and thatdis-' closed in the aforesaid copending application.

The general principles relating to the provision, first, of ample mixingvolume, second, of means to heat the mixer chamber, and, third, of meansto facilitate the flow of nitric acid vapor from the retort tubes to thedehydrating tower, may be applied by apparatus differing from thatpreviously described, and a modified arrangement is shown in Fig. 2.This arran ement emplo s only a single-mixer tube M r the mixer chamberbut the diameter of this tube is substantially greater than that of theretort tubes R. In 7 consequence of this, a volume of acid amplysuflicient to insure thorough mixing of the.

sulphuric and nitric acids may readily be provided without necessitatinga high liquid evel in the tube. It therefore follows that Fig. 3, inwhich the mixer chamber M consists partially of a heated tube 60 andpartially of an unheated chamber 62, most conveniently obtained byutilizing the bottom of the dehydrating tower D. In this arrangement themixer chamber has a volume far greater than that of the liquid contentin a retort tube and, in consequence, thorough mixing and absence ofstratification'into layers of the nitric and sulphuric acids is insured.With a this arrangement the tube 60 may be heated or left unheated, asdesired. If unheated, the arrangement improves upon the pr1orarrangement in providing augmented mixer chamber volume. It heated,additional ad vantage is obtained in the further utilization of tubesurface. The liquid levelin thetube 60 is kept relatively low in orderto provide ample space above the liquid for; the free flow ofthe entirenitric acid vapor output of the retort system. This lowering of thelevel of the acid'mixture in tube 60 is not deleterions because themixer chamber volume available is sufficient to insure thorough mixingdue to the auxiliary chamber 62.

The arrangements disclosed in Figs. land 3 have the advantage over thatdisclosed in Fig. 2 of employing uniform pipes, jackets and fittingsthroughout the system, which simplifiesthe problem of replacement and ofproviding spare parts for maintenance.

However, in any case where two sizes of pipes and fittings are anywayavailable due to requirements at other points in the manufacturingplant, the arrangement illustrated in Fig.

"T 40 2 may prove desirable.

The method of my invention, the mode of constructing suitable apparatusfor the practice ofthe same, and the many advantages of the invention,will, it is believed, be apparent from the foregoing descriptionthereof. The

details of the operation of the entire concentration system have notbeen set forthbecause these, for the most part, coincide with thedisclosure of the copending application previously identified, andthepresent system, ex-

cept in the particulars previously outlined in detail, does not affectthe operation there described. In the present arrangement thoroughmixing of the nitric and sulphuric acids is insured, heating surface isconserved, thereby increasing the plant capacity, and the transfer ofnitric acid vapor from the retort tubes and from the mixer chamber tothe dehydrating tower is facilitated.

It will be apparent that while I have shown and described my inventionin the preferred forms, many changes and modifications may be made inthe structures disclosed without departing from the spirit of theinvention, defined in the following claims.

I claim:

1. In the operation of a nitric acid concentrator comprising a series ofheated retort tubes, the method which includes mixing the dilute nitricacid with sulphuric acid in a body of liquid having a volumesubstantially greater than that of the liquid content in a retort tubein order to insure thorough mixing of the acids, and assing theresulting acid mixture through t 1e retort tubes. 5

2. In the operation of a nitric acid concentrator comprising a series ofheated retort tubes, the method which includes mixing the dilute nitricacid with sulphuric acid in a; body of liquid having a volumesubstantially greater than that of the liquid content in a retort tubein order to insure thorough mixing of the acids, externally heating atleast a portion of the initially mixed nitric and sulphuric acids, andpassing the resulting acid mixture through the retort tubes.

3.- In the operation of a nitric acid concentrator comprising a seriesof heated retort tubes and a dehydrating tower, the method r whichincludes mixing the dilute nitric acid with sulphuric acid in a body ofliquid having a volume substantially greater than that of the liquidcontent in a retort tube, externally heating at least a portion of theinitially mixed nitric and sulphuric acids, passing 1 5 the resultingacid mixture through the retort tubes, and conducting the resultingnitric acid vapor and any water vapor incidentally evolved therewith tothe dehydrating tower for passage in counter-current relation to thesulphuric acid going into the acid mixture.

4. In the operation of a nitric acid concentrator comprising a series ofheated retort tubes and a dehyrating tower, the method which includesmixing the dilute nitric acid 165' with sulphuric acid, passing theresulting acid mixture through the retort tubes in order to evolvenitric acid vapor, conducting the resulting nitric acid vapor and anywater vapor incidentally evolved therewith to the dehydrating tower,externally heating at. least a portion of the initially mixed nitric andsulphuric acids, and independently conducting the'resulting nitric acidvapor and, any water vapor incidentally evolved therewith to thedehydrating tower.

5. In the operation of'a nitric acid concentrator comprising a series ofheated retort tubes and a dehydrating tower, the method which includesmixing the dilute nitric acid with sul huric acid in abody of liquid having a vo-ume substantially greater than that. of the liquid content in aretort tube in order to insure thorough mixing of the acids, externallyheating at least a portion of the initially mixed nitric and sulphuricacids, conducting the resulting nitric acid vapor and any water vaporincidentally evolved therewith to the dehydrating tower, passing the,

acid mixture through the retort tubes in or- 3 der evolve nitricacidvapor, independent.- ly conducting the resulting nitric acid vaporand any water vapor incidentally evolved therewith to the dehydratingtower, and

. passing the vapor through the tower in countercurrent relation to thesulphuric acid going into the acid mixture.

6. A nitric acid separation or/and concentrationsystem comprising aplurality of retort tubes, means to heat the retort tubes, a

mixer chamber having a volume substantially greater than the volume of aretort tube connected to the retort tubes, and sulphuric acid and nitricacid supply tanks feeding into 5 said mixer chamber.

- .7; A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected in series, means to heat the retorttubes, a dehydrating tower,vand a mixer chamber having a volumesubstantial.-

ly greater than the volume of a retort tube connected between the retorttubes and the dehydrating tower.

8. A nitric acid separation or/and concen- 125 tration system com risinga plurality of re-.

" tort tubes connect in series and provided at their discharge ends withmeans for estab lishing the liquid levels therein, means to heat theretort tubes, a dehydrating tower,

and amixer chamber between the retort tubes and the dehydrating towerand having a volume substantially greater than the volume of a retorttube.

9. A nitric acid separation or/and concentration system comprising aplurality of retort tubes, a mixer chamber connected to the retort tubesand havin a volume substantial- V ly greater than that o a retort tube,sulfuric acid and nitric acid supply tanks feeding into said mixerchamber, and means to heat 5 retort tubes connected in series, a dehy erchamber. a a

11. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected inseries and provided 5 at theirdischarge ends with means for estab lishing the liquid levels therein, adehydrating tower, a mixer chamber between the retort tubes and thedehydrating tower and having a volume substantially greater than that ofa retort tube, means to heat the retort tubes, and additional means toindependently heat at least a portion of the mixer chamber. I

12. A nitric acid separation or/and concentration system comprising aplurality of retort tubes and at least a portion of the mix-. I

retort tubes connected in series, means to heat the retort tubes, 0.dehydrating tower, a mixer chamber connected between the retort tubesand the dehydrating tower and having a volume substantially greater thanthat of a retort tube, and mcansto facilitate the feed of nitric acidvapor from the retort tubes to the dehydrating tower.

13. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected in series, means to heat the retorttubes, a dehydrating tower, a mixer chamber connected between the retorttubes and the dehydrating tower and having a volume substantiallygreater than that of a retort tube, means to heat the mixer chamher, andmeans to facilitate the feed of nitric acid vapor from the retort tubesand mixer chamber to the dehydrating tower.

14. A separation or/ and concentration system comprising a retort, a.dehydrating tower, mixer means connected between the retort and thedehydrating tower, means to conduct vapor from the retort to thedehydrating tower, and means to independently conduct vapor from themixer means to the dehydrating tower. 15. A separation or/andconcentration system comprising a retort, a dehydrating tower, mixermeans connected between the retort and the dehydrating tower, means toconduct vapor from the retort to the dehydrating tower, means to heatthe mixer means, and means to independently conduct vapor from the mixermeans to the dehydrating tower;

16. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected in series, means to heat the retorttubes, a dehydrating tower, a mixer chamber connected between the retorttubes and the dehydrating tower, means to conduct the nitric acid vaporfrom the retort tubes directly to the dehydrating tower, and means toconduct nitric acid vapor from the mixer chamber to the dehydratingtower:

independently of the feed of nitric acid vapor from the retort tubes tothe dehydrating tower. g

17. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected in series. means to heat the retorttubes, a dehydrating tower, a mixer chamber connected between theretorttubes and the dehydrating tower and having a volume substantiallygreater than that of a retort tube, means to conduct the feed of nitricacid vapor from the retort tubes direct- 1y to the dehydrating tower.and means to conduct nitric acid vapor from the mixer chamber to thedehydrating tower independently of the feed of nitric acid vapor fromthe retort tubes to the dehydrating tower.

18. A nitric acid separation or/and concentration system comprising aplurality of heat the retort tubes, a dehydrating tower,

a mixer chamber connected between the retort tubes and the dehydratingtower, means to conduct the nitric acid vapor from the retort tubesdirectly to the dehydrating tower, means to heat the mixer chamber, andmeans to conduct nitric acid vapor from the mixer chamber to thedehydrating tower independently of the feed of nitric acid vapor fromthe retort tubes to the dehydrating tower.

19. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected in series and provided at theirdischarge ends with means for determining the liquid levels therein,means to heat the retort tubes, adehydrating tower, a mixer chamberconnected between the retort tubes and the dehydrating tower and havinga volume substantially greater than that of a retort tube, means toconduct the nitric acid vapor from the retort tubes directly to thedehydratingtower, means to heat the mixer chamber, and means to conductnitric acid vapor from the mixer chamber to the dehydrating towerindependently of the feed of nitric acid vapor from the retort tubes tothe dehydrating tower.

20. A nitric acid separation or/and concentration system comprising aplurality of retort tubes connected series, a dehydrating tower, mixermeans connected between the retort tubes and the dehydrating tower,means to conduct nitric acid vapor from the mixer means to thedehydrating tower, and i a pipe bypassing the mixer means and connectingthe retort tubes with the dehydrating tower.

Signed at Buffalo in the county of Erie and State of New York this 8thday of May SAMUEL F. SPANGLER.

